Bottom Line:
Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores.Fe solubility was very variable (1-42%) during the interval, and frequently higher than typically assumed by models.Soluble aerosol Fe fluxes to Dome C at the LGM (0.01-0.84 mg m(-2) per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply.

ABSTRACTRelief of iron (Fe) limitation in the Southern Ocean during ice ages, with potentially increased carbon storage in the ocean, has been invoked as one driver of glacial-interglacial atmospheric CO2 cycles. Ice and marine sediment records demonstrate that atmospheric dust supply to the oceans increased by up to an order of magnitude during glacial intervals. However, poor constraints on soluble atmospheric Fe fluxes to the oceans limit assessment of the role of Fe in glacial-interglacial change. Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores. Fe solubility was very variable (1-42%) during the interval, and frequently higher than typically assumed by models. Soluble aerosol Fe fluxes to Dome C at the LGM (0.01-0.84 mg m(-2) per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply.

f2: Variability in fluxes and chemistry of aerosol Fe deposited to Antarctica shown with other climatic parameters.(a) Fluxes of total and soluble (pH ∼5.3, seawater, pH ∼1 (ref. 20)) aerosol Fe, and Fe solubility across the LGM interval from the EPICA Dome C core. (b) Comparison of aerosol Fe solubility at pH ∼5.3 and in natural seawater (pH ∼8) from EDC ice of identical LGM age. Dashed line indicates 1:1. (c) Fluxes of total and soluble (pH ∼5.3) aerosol Fe and Fe solubility from MIS 2–3 of the Berkner Island Core. The grey bar denotes the LGM and the orange bars denote Antarctic warm events. Data points represent two measurements of a single sample, and errors are smaller than the size of points. All data are shown on the EDC3 age scale47. See Methods section for details of other climatic parameters, and details of conversion of Berkner age to EDC3.

Mentions:
Aerosol Fe solubility and calculated total and soluble Fe fluxes from EDC and Berkner ice cores are shown compared with other ice-core parameters in Figs 2, 3, 4, with a comparison of Fe solubility in EDC ice of LGM age at pH ∼5.3 and in seawater shown in Fig. 2b. The data are also available in Supplementary Data.

f2: Variability in fluxes and chemistry of aerosol Fe deposited to Antarctica shown with other climatic parameters.(a) Fluxes of total and soluble (pH ∼5.3, seawater, pH ∼1 (ref. 20)) aerosol Fe, and Fe solubility across the LGM interval from the EPICA Dome C core. (b) Comparison of aerosol Fe solubility at pH ∼5.3 and in natural seawater (pH ∼8) from EDC ice of identical LGM age. Dashed line indicates 1:1. (c) Fluxes of total and soluble (pH ∼5.3) aerosol Fe and Fe solubility from MIS 2–3 of the Berkner Island Core. The grey bar denotes the LGM and the orange bars denote Antarctic warm events. Data points represent two measurements of a single sample, and errors are smaller than the size of points. All data are shown on the EDC3 age scale47. See Methods section for details of other climatic parameters, and details of conversion of Berkner age to EDC3.

Mentions:
Aerosol Fe solubility and calculated total and soluble Fe fluxes from EDC and Berkner ice cores are shown compared with other ice-core parameters in Figs 2, 3, 4, with a comparison of Fe solubility in EDC ice of LGM age at pH ∼5.3 and in seawater shown in Fig. 2b. The data are also available in Supplementary Data.

Bottom Line:
Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores.Fe solubility was very variable (1-42%) during the interval, and frequently higher than typically assumed by models.Soluble aerosol Fe fluxes to Dome C at the LGM (0.01-0.84 mg m(-2) per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply.

ABSTRACTRelief of iron (Fe) limitation in the Southern Ocean during ice ages, with potentially increased carbon storage in the ocean, has been invoked as one driver of glacial-interglacial atmospheric CO2 cycles. Ice and marine sediment records demonstrate that atmospheric dust supply to the oceans increased by up to an order of magnitude during glacial intervals. However, poor constraints on soluble atmospheric Fe fluxes to the oceans limit assessment of the role of Fe in glacial-interglacial change. Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores. Fe solubility was very variable (1-42%) during the interval, and frequently higher than typically assumed by models. Soluble aerosol Fe fluxes to Dome C at the LGM (0.01-0.84 mg m(-2) per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply.